EDITING C-13-NMR SPECTRA OF MEMBRANES

We report the carbon-13 'magic-angle' sample-spinning nuclear magnetic resonance (NMR) spectra of several lipid-water systems, under a varie ty of radiofrequency excitation conditions. Our results show that comp lex lipid or membrane spectra can be greatly simplified by using 'spec tral editing' techniques. For example, in a 1,2-dimyristoyl-sn-glycero -3-phosphocholine (DMPC)-water mesophase, the glycerol (C-1, C-2 and C -3) carbons are readily distinguished from the headgroup C(alpha), C(b eta) and C(gamma) carbons, on the basis of their mix-time behavior in a cross-polarization (CP) experiment, while in the more complex DMPC/c holesterol-water system, many of the more rigid cholesterol carbon res onances can be edited from the phospholipid peaks. In very complex sys tems, such as human myelin membranes, editing permits the unambiguous observation of the mobile lipid headgroup carbon resonances, as well a s the much more rigid sterol ring carbons. We also report the observat ion of a large differential CP due to C-H vector 'magic-angle' orienta tional effects in the DMPC/desipramine system. Thus, both motional or orientational reduction of the C-H dipolar interaction can lead to con siderable simplifications of complex membrane spectra, and are of inte rest from both spectral assignment and membrane dynamics aspects.